Usually when quantum phenomena are studied experimentally, the experiments are performed upon large ensembles of particles, since such systems are more readily accessible via experiment. These two gentlemen, however, pioneered methods for performing experiments involving the study of the quantum behavior of individual particles. This is no small feat.

The biggest challenge here is that of measuring the quantum state of an individual particle without destroying that state. In general, measuring some quantum property of a photon (such as its polarization) tends to require destroying the photon. The work recognized by this prize works around that.

Serge Haroche’s Work

Serge Haroche and his colleagues trapped microwave photons in a cavity lined with superconducting mirrors. (Since the mirrors are superconducting, they exclude magnetic fields, which bring the mirrors closer to being perfect reflectors.) This effectively allowed photons trapped within the cavity to bounce around within it billions of times, containing the photons for a prolonged period of time (more than a tenth of a second, which is practically an eternity in the quantum world).

Rydberg atoms (atoms whose electrons are in such an excited state that they are barely bound to the nuclei) were then sent through the chamber one at a time. A comparison of the atoms’ states before and after their transit of the photon trap allowed researchers to non-distructively determine the states of the photons within.

David Wineland’s Work

Earlier researchers had pioneered the technique of using lasers to cool and trap individual ions, work which was recognized with the 1997 Nobel Prize in Physics. (Of of the recipients of that prize was Steven Chu, currently the US Secretary of Energy.) Wineland and his colleagues took this a step further, devising methods for manipulating the ions and measuring their quantum states. The trapped ion sits at the intersection multiple oscillating electric fields, rising up and down periodically like a cork on a rippling pond. The control laser is then used to probe the ion’s quantum properties.

By the way, I should point out that Wineland and his cohorts have more recently used these techniques to develop an atomic clock so accurate that it can sense the slight relativistic time dilation caused by simply lowering the clock a mere 30cm further into the Earth’s gravity well.

Where to from Here?

The most immediate application of this work is in the field of quantum computing. In order to ever be able to successfully build quantum computers, the ability to poll, set, and maintain the quantum states of individual particles without quantum decoherence (the loss of quantum order due to interactions with other particles and fields in the environment) setting in is of paramount importance.